X-ray systems are frequently used for imaging for the purposes of diagnostic examination and for interventions, for example in the areas of cardiology, radiology and surgery. These x-ray systems generally comprise a C-arm, on which an x-ray tube and x-ray detector are disposed opposite one another, a patient couch and a system control and display unit. Systems with two planes, i.e. with two C-arms, are also used in interventional radiology.
Monoplane systems, i.e. x-ray systems with one tube and one detector, are used both for diagnostic purposes, e.g. during native vessel display using contrast agents, digital subtraction angiography DSA, and cone-beam computed tomography for generating volumetric datasets, and during interventions such as for example percutaneous transluminal coronary angioplasty PTCA, balloon dilation, coiling, embolization and ablation.
Biplane systems are used when it is necessary to display a vessel or aneurism for example from different angles virtually simultaneously, such as for an intervention, to give a better picture of actual spatial conditions. Fields of application include for example neuroradiology, cardiological electrophysiology and pediatric cardiology.
Displaying an organ from two projection directions using two detector planes, in other words a biplane system, however does not permit the generation of a spatial or 3D impression of different structures of an organ, for example the intersection of vessels or position of an aneurism, or other objects. Any perception of foreground and background is only possible to a limited degree.
One method of obtaining a spatial impression of an object is offered by what is known as stereoscopy. German Wikipedia describes stereoscopy by way of example as follows: “Stereoscopy (Greek stereos=space/spatial, firm/solid−skopeo=to look at) is the reproduction of images with a spatial impression of depth which is physically not present. Stereoscopy is also incorrectly referred to colloquially as “3D”, even though it only involves two-dimensional images which convey a spatial impression” and also “The principle is based on the fact that, like all primates and most predators, people look at their surroundings simultaneously from two angles through their two eyes. This allows their brain to assign a distance efficiently to all viewed objects, giving a three-dimensional image of said surroundings, without having to keep moving the head. Stereoscopy simply deals with bringing different two-dimensional images from two slightly differing viewing angles to the left and right eyes. The methods used to do this however vary.”
Stereoscopy can also be used in the field of x-ray imaging. One embodiment is described for example in U.S. Pat. No. 4,769,701. Two x-ray focuses are used here, being positioned a certain distance from one another, their central beams intersecting in the recording plane. These generate radiation one after the other and this is registered on an x-ray detector. The images, each of which was recorded from a different perspective, are then supplied separately by a dedicated apparatus to the left and right eye respectively of a viewer. This produces the three-dimensional impression.
When using stereoscopy in medical x-ray imaging there are certain objects that have to be achieved. One object relates to the possible movement of an object or organ. During intervention-related and similarly diagnostic examinations there are for example organs which are non-moving, for example fixed craniums or extremities. Other organs exhibit only slight movement, for example the liver. Others are in constant motion, with sometimes significant amplitudes, for example the heart or aorta. Objects such as catheters, wires or coils, are moved during intervention-related examinations. And finally there is motion caused by a patient moving or a patient couch or the C-arm of the x-ray device being displaced. Possible applications are for example interventional cardioangiography or electrophysiology, e.g. when the endocardium is punctured using a transseptal needle. With moving objects however it should be ensured that imaging takes place virtually simultaneously from the two projection directions, so that a time correlation is ensured between the two projection images. If the differences between the two images are not only due to the different projection settings, but are also due to movement, an identical spatial assignment of the object in the stereo image is not possible. Simultaneous recording of the two images is not possible in principle due to the one x-ray detector, so there is always a certain time interval between the recording of the two images. This means that there is deterioration in image quality for moving objects.